大约有 19,000 项符合查询结果（耗时：0.0525秒） [XML]
MySQL order by before group by
...desc
If you have the following sample data:
CREATE TABLE wp_posts
(`id` int, `title` varchar(6), `post_date` datetime, `post_author` varchar(3))
;
INSERT INTO wp_posts
(`id`, `title`, `post_date`, `post_author`)
VALUES
(1, 'Title1', '2013-01-01 00:00:00', 'Jim'),
(2, 'Title2', '2...
Check if element exists in jQuery [duplicate]
...an element exists if the element is created by .append() method?
$('elemId').length doesn't work for me.
8 Answers
...
How to drop a table if it exists?
...le does not exist).
Instead, for a permanent table you can use
IF OBJECT_ID('dbo.Scores', 'U') IS NOT NULL
DROP TABLE dbo.Scores;
Or, for a temporary table you can use
IF OBJECT_ID('tempdb.dbo.#T', 'U') IS NOT NULL
DROP TABLE #T;
SQL Server 2016+ has a better way, using DROP TABLE IF E...
Canvas width and height in HTML5
Is it possible to fix the width and height of an HTML5 canvas element?
4 Answers
4
...
WHERE vs HAVING
...level aliases in GROUP BY, ORDER BY and HAVING.
And are there any downsides instead of doing "WHERE 1" (writing the whole definition instead of a column name)
If your calculated expression does not contain any aggregates, putting it into the WHERE clause will most probably be more efficient.
...
How do I use the conditional operator (? :) in Ruby?
...some extra junk after it), but they are not required in the last case as said issue does not arise.
You can use the "long-if" form for readability on multiple lines:
question = if question.size > 20 then
question.slice(0, 20) + "..."
else
question
end
...
Is it possible to use argsort in descending order?
Consider the following code:
9 Answers
9
...
for each loop in Objective-C for accessing NSMutable dictionary
...
for (NSString* key in xyz) {
id value = xyz[key];
// do stuff
}
This works for every class that conforms to the NSFastEnumeration protocol (available on 10.5+ and iOS), though NSDictionary is one of the few collections which lets you enumerate keys...
Why would an Enum implement an Interface?
...ple here is wrong, since Enum already implements that. You can't even override it.
A better example is having an interface that defines, let's say, a data type. You can have an enum to implement the simple types, and have normal classes to implement complicated types:
interface DataType {
// met...
Is it possible to deserialize XML into List?
...c List<User> Items {get;set;}
}
public class User
{
[XmlElement("id")]
public Int32 Id { get; set; }
[XmlElement("name")]
public String Name { get; set; }
}
static class Program
{
static void Main()
{
XmlSerializer ser= new XmlSerializer(typeof(UserList));
...